Sheet feeding apparatus and image forming apparatus

ABSTRACT

A sheet feeding apparatus including: a separation claw for restraining both end portions of leading edges of sheets in a width direction orthogonal to a sheet feeding direction, the sheets having reached a sheet feeding position, and separating, one by one, the sheets fed by a pickup roller; and a photosensor detecting that the separation claw has reached a separation position for separating the sheets when a sheet stacking board is raised to detect that the sheets have reached the sheet feeding position, in which the separation claw, which is movable in an up-and-down direction, is moved to the separation position, the photosensor detects that the sheets supported by the sheet stacking board have reached the sheet feeding position of being feedable by the pickup roller, by rise of the sheet stacking board.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding apparatus and an imageforming apparatus, in particular, a sheet feeding apparatus and an imageforming apparatus, which separate sheets one by one by using aseparation claw and feed the separated sheets.

2. Description of the Related Art

In recent years, an image forming apparatus such as a printer, a copyingmachine, or a facsimile machine includes a sheet feeding apparatus forseparating sheets one by one and feeding the separated sheets to animage forming portion. As the above-mentioned sheet feeding apparatus,for example, there is known an apparatus configured to raise and lower asheet supporting portion, which has the sheets stacked thereon, by drivefrom a driving source such as a motor. In the sheet feeding apparatus,the sheet supporting portion is raised so that an uppermost sheet of thestacked sheets can be located at a position in a height direction (thatis, sheet feeding position), where it becomes possible to feed thesheets by a feed roller.

Then, in order to continuously feed the sheets, it is necessary to keepthe height of the uppermost sheet on the sheet supporting portion, atsuch a height (sheet feeding position) at which the uppermost sheet canbe fed by the feed roller. Therefore, heretofore, the sheet feedingapparatus is provided with an optical sensor and a sensor flag. Thesensor flag pushed up by the uppermost sheet shields the optical sensorfrom sensor light, to thereby detect that the uppermost sheet hasreached the sheet feeding position. Then, the optical sensor detectsthat the height of the uppermost sheet is lowered from the sheet feedingposition as a result that the sheets are fed, and based on suchdetection, the rise of the sheet supporting portion is controlled sothat the height of the uppermost sheet can be maintained at the sheetfeeding position. This technology is disclosed in Japanese PatentApplication Laid-Open No. 2003-165633.

Further, heretofore, as a sheet feeding apparatus configured to feedsheets prone to be adhered to one another, there has been an apparatusincluding a mechanism for loosening a sheet bundle, which is stacked inorder to be fed, by blowing air thereto. In this case, in order toenable surely a feed of the sheets prone to be adhered to one another,for example, air is blown by air blowing means to a side end of an upperportion of the sheet bundle stacked on the sheet supporting portion, andair is allowed to pass through among the sheets, so that the sheets arereleased from being adhered to one another. Note that, in the sheetfeeding apparatus as described above, a sheet holding-down member forsuppressing flotation of the sheets to which air is blown is provided.This technology is disclosed in Japanese Patent Application Laid-OpenNo. 2008-87906.

However, in the conventional sheet feeding apparatus, when the sheetsare sequentially fed, a height of the sheet bundle is thereby lowered,and following this, the sensor light of the optical sensor becomesunshielded, then the sheet supporting portion rises. At this time, whenair is blown to trailing edges of the sheets, a sheet surface againstwhich the sensor flag abuts floats up because the sheet holding-downmember is arranged at a position apart from the sheet surface. Then, ina case where the sheet surface against which the sensor flag abutsfloats up as described above, then the sensor flag is pushed up, thesensor light becomes shielded before the uppermost sheet reaches thesheet feeding position, and the uppermost sheet cannot be held at thesheet feeding position.

Further, for example, in a case where leading edge portions of thesheets stacked on the sheet supporting portion are curled upward, aheight of the sheet surface against which the sensor flag abuts and asurface height of the leading edges of the sheets differ from eachother. In this case, when a height of the sheet supporting portion iscontrolled based on a signal from the optical sensor, the leading edgesof the sheets become located more upward than the sheet feeding positionin terms of height. Therefore, when the sheets are fed in this state,there is apprehension that the leading edges of the sheets cannotsmoothly enter a nip between conveyor rollers located downstream thereofresulting in sheet jamming.

SUMMARY OF THE INVENTION

In view of the above-mentioned circumstances, the present invention hasbeen made, and therefore, it is an object of the present invention toprovide a sheet feeding apparatus and an image forming apparatus, whichare capable of surely detecting that the sheets have reached the sheetfeeding position.

According to the present invention, there is provided a sheet feedingapparatus configured to feed sheets, including:

a rising and lowering sheet supporting portion configured to support thesheets;

a raising and lowering mechanism configured to raise and lower the sheetsupporting portion;

a feed roller configured to feed out an uppermost sheet of the sheetssupported by the sheet supporting portion;

a detecting portion configured to detect the uppermost sheet of thesheets supported by the sheet supporting portion;

a separation claw, which is movable up and down and configured toseparate, one by one, the sheets fed by the feed roller, by restraininga side end of leading edges of the sheets in a width directionorthogonal to a sheet feeding direction; and

-   -   a control portion configured to control the raising and lowering        mechanism based on a detection by the detecting portion,

wherein the detecting portion is arranged to detect a position of theseparation claw, and the control portion controls the raising andlowering mechanism based on the detection by the detecting portion sothat the uppermost sheet of the sheets supported by the sheet supportingportion is located at a position of being feedable by the feed roller.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a schematic configuration of a laser beamprinter as an example of an image forming apparatus including a sheetfeeding apparatus according to a first embodiment of the presentinvention.

FIG. 2 is a view illustrating a configuration of a sheet feeding deck asthe sheet feeding apparatus.

FIG. 3 is a block diagram for performing control of a sheet stackingboard provided in the sheet feeding apparatus.

FIG. 4 is a view illustrating a separation claw provided on the sheetfeeding deck.

FIG. 5 is a view illustrating a configuration of a sheet feeding deck asa sheet feeding apparatus according to a second embodiment of thepresent invention.

FIG. 6 is a view illustrating another configuration of the sheet feedingdeck.

DESCRIPTION OF THE EMBODIMENTS

A description will be provided below in detail of embodiments forimplementing the present invention with reference to the accompanyingdrawings. FIG. 1 is a view illustrating a schematic configuration of alaser beam printer as an example of an image forming apparatus includinga sheet feeding apparatus according to a first embodiment of the presentinvention. In FIG. 1, the laser beam printer 1, a laser beam printermain body 1A (hereinafter referred to as a printer main body), and adeck-type sheet feeding apparatus 2 (hereinafter referred to as a sheetfeeding deck) mounted under the printer main body 1A are illustrated. Animage forming portion 1B is provided in the printer main body 1A, andforms an image by an electrophotographic method. The image formingportion 1B includes: a photosensitive drum 14 on which a toner image isformed; a laser exposure device 17 as a laser exposure optical systemconfigured to irradiate the photosensitive drum 14 with a laser beamaccording to an image signal; and a transfer roller 15 configured totransfer, to a sheet S, the toner image formed on the photosensitivedrum 14. The photosensitive drum 14 is incorporated in a processcartridge 13 detachably mounted to the printer main body 1A. In a lowerportion of the printer main body 1A, a cassette 20 configured to stackand contain the sheets S therein is detachably mounted to the printermain body 1A, and the sheets S contained in the cassette 20 areappropriately fed out in order from an uppermost one by a pickup roller21 provided in the printer main body 1A.

In FIG. 1, a feed roller 23 is provided in the printer main body 1A, anda retard roller 24 rotates at a predetermined torque through a torquelimiter (not shown) in a direction of returning the sheets conveyed bythe feed roller 23. By the feed roller 23 and the retard roller 24provided in the printer main body 1A, the sheets S fed out by the pickuproller 21 are separated and fed one by one. Pairs of conveyor rollers 11and 12 are provided in the printer main body 1A, and the pairs ofconveyor rollers 11 and 12 sequentially receive the sheets S fed by thefeed roller 23, and convey the received sheets S toward a registrationroller pair 25. The sheet S on which a toner image is transferred issubjected to heating and pressing treatments at the time of passingthrough a fixing device 16, so that the toner image is fixed to thesheet S.

In the laser beam printer 1 configured as described above, when an imageforming operation is started, first, the photosensitive drum 14 isirradiated with light according to the image signal by the laserexposure device 17, and then a latent image is formed on thephotosensitive drum by such irradiation of the light according to theimage signal. Next, this latent image is developed by toner contained inthe process cartridge 13, to thereby form the toner image (visibleimage) on the photosensitive drum. In parallel with such a toner imageforming operation, for example, the sheets S stacked on the cassette 20are fed out in order from the uppermost one by the rotation of thepickup roller 21. After that, the sheets S are separated and conveyedone by one by a separation portion including the feed roller 23 and theretard roller 24.

After that, the sheet S fed by the feed roller 23 is conveyed toward thestandstill registration roller pair 25 by the pairs of conveyor rollers11 and 12 provided in the printer main body 1A, and then leading edge ofthe sheet S is allowed to abut against a nip portion of the registrationroller pair 25 so that a loop is formed in the sheet S, to therebycorrect the skew feed of the sheet S. After that, the registrationroller pair 25 starts to rotate in synchronization with the image formedon the photosensitive drum 14, and conveys the sheet S to a nip portionbetween the photosensitive drum 14 and the transfer roller 15 oppositethereto. Further, when the sheet S is fed from the sheet feeding deck 2configured as described later, the sheet S is also conveyed to atransfer portion comprising the photosensitive drum 14 and the transferroller 15, by the registration roller pair 25 in synchronization withthe image formed on the photosensitive drum 14. In the transfer portion,a bias is applied to the transfer roller 15, so that the toner image istransferred to the sheet S which comes from the cassette 20 or to thesheet S which comes from the sheet feeding deck 2. After that, the sheetS on which the toner image is thus transferred is conveyed to the fixingdevice 16, and is pressed and heated in the fixing device 16, so thatthe toner image is fixed thereto. After that, the sheet S is deliveredby a delivery roller 18 to a delivery tray 19 provided in an upperportion of the printer main body.

The sheet feeding deck 2 includes a sheet stacking board 55 that isprovided, as being capable of rising and lowering, in a sheet storage 2a as a sheet containing portion configured to contain the sheets Stherein, and is a sheet supporting portion configured to stack andsupport a bundle of the sheets S. Further, the sheet feeding deck 2includes a trailing edge regulating plate 56 configured to regulate aposition of a trailing edge as an upstream side edge of a sheet bundleSa in a sheet feeding direction. Here, the sheet bundle Sa is stacked onthe sheet stacking board 55. Further, the sheet feeding deck 2 includesa door 2 c to be opened at the time of stacking the sheet bundle Sa onthe sheet stacking board 55. The door 2 c is arranged on a front side ofthe printer main body 1A. When the door 2 c is opened, the sheets S canbe loaded and unloaded from an operation side of the printer main body1A.

Further, as illustrated in FIG. 2, the sheet feeding deck 2 includesside regulating plates 57 and 58 as a pair of regulating membersconfigured to regulate a position of the sheet bundle Sa in a widthdirection orthogonal to the sheet feeding direction. Here, the sheetbundle Sa is stacked on the sheet stacking board 55. The sheet stackingboard 55 is suspended through wires 60 a to 60 d, each having an endfixed to a wire winding shaft 59. By rotating the wire winding shaft 59forward and reverse by a raising and lowering motor (not shown), thewires 60 a to 60 d are wound in and wound off, to thereby move (raiseand lower) the stacking board 55 in an up-and-down direction. In thisembodiment, a raising and lowering mechanism 60 configured to raise andlower the sheet stacking board 55 includes: the raising and loweringmotor (not shown); the wires 60 a to 60 d; and the wire winding shaft59.

Further, the sheet feeding deck 2 includes a sheet feeding portion 2 bconfigured to feed out an uppermost sheet S1 of the sheet bundle Sastacked on the sheet stacking board 55. The sheet feeding portion 2 bincludes a pickup roller 51 as a feed roller configured to feed out thesheets S1, which are stacked on the sheet feeding board 55, in orderfrom the uppermost one. Further, the sheet feeding portion 2 b includes:a feed roller 52 and a retard roller 53, which serve as a separationportion configured to separate and feed one by one the sheets S1 fed outby the pickup roller 51; and a conveyor roller 54 configured to conveythe sheet S1, which is separated one by one by the separation portion,to the printer main body 1A. Still further, in the vicinity of thetrailing edge regulating plate 56, a fan 30 as an air blowing portionconfigured to blow air toward a trailing edge of an upper portion (inthe vicinity of the uppermost sheet S1) of the sheet bundle Sa isarranged.

Further, as illustrated in FIG. 2, a drive gear 103 is driven by a drivemotor Md illustrated in FIG. 3, and the drive gear 103 is fixedlyattached to a roller shaft 104. Then, at the time of feeding the sheets,the drive gear 103 is driven, to thereby rotate the roller shaft 104.Following the rotation of the roller shaft 104, a moment in a directionof allowing the pickup roller 51 to abut against the sheets S1 isgenerated in a pick arm 106 from the roller shaft 104 taken as afulcrum. In this manner, the pickup roller 51 rotatably held on arotation end of the pick arm 106 abuts against the sheets S1. By reverserotation of the roller shaft 104, a moment in a direction of moving thepickup roller 51 to be spaced apart from the sheets S1 is generated inthe pick arm 106, and the pickup roller 51 is spaced apart from thesheets S1.

Further, a sheet feeding pressure is changed depending on a frictioncoefficient between the sheet S1 and the pickup roller 51, and areaction force acts on the pickup roller 51 in a direction reverse tothe sheet feeding direction, by reaction force from the sheet S1 at thetime of feeding the sheet. Then, the roller shaft 104 (rotation fulcrum)of the pick arm 106 is arranged upstream in the sheet feeding direction,and hence a component force in a direction of being brought intopressure contact with the sheet S1 is generated in the pickup roller 51by the reaction force that acts on the pickup roller 51. The sheetfeeding pressure is set based on the component force and the own weightof the pickup roller 51. Therefore, a force by which the pickup roller51 is brought into pressure contact with the sheet at the time offeeding the sheet S1 is changed depending on the friction coefficientbetween the sheets S1 and the pickup roller 51. For example, for thesheets S1 in which a friction coefficient thereamong is small andfeeding with small feeding force is necessary, the sheet feedingpressure is also reduced, and double feeding becomes less likely tooccur. On the contrary, for the sheets S1 in which the frictioncoefficient thereamong is large and a large feeding force is necessary,the sheet feeding pressure is also increased, and an occurrence of afeeding failure of the sheets can be prevented. As described above, thesheet feeding pressure with which the pickup roller 51 abuts against thesheets S1 is generated in such a manner that the pickup roller 51 isbrought into pressure contact with the sheet S1 by the moment generatedin the pick arm 106 when a driving force is transmitted to the pick arm106 and the reaction force when the pickup roller 51 feeds the sheet S1.

Then, in the sheet feeding deck 2 configured as described above, whenthe stacking of the sheet bundle Sa onto the sheet stacking board 55 isended, and the door 2 c is closed, a detection sensor (not shown)detects the close of the door 2 c. Based on the detection of thedetection sensor, a control portion C illustrated in FIG. 3 rotates araising and lowering motor ML. In this manner, the wire winding shaft 59rotates so that the wires 60 a to 60 d are wound in, and the sheetstacking board 55 is raised. After moving to a position capable offeeding the uppermost sheet S1, the sheet stacking board 55 iscontrolled to rise and lower, so as to maintain the position, by thecontrol portion C based on a signal coming from a photosensor 61 to bedescribed later. After that, the feeding of the sheets S1 is started bythe pickup roller 51 that has abutted against the sheets S1 raised tothe position (hereinafter referred to as a sheet feeding position)capable of feeding the sheets S1 by the pickup roller 51. Note that, thesheet feeding position is located within a certain range in the heightdirection capable of feeding the sheets, and if the uppermost sheet islocated within the range, it is possible to feed the uppermost sheetbecause the sheet feeding pressure generated between the pickup roller51 and the uppermost sheet remains within the range capable of feedingthe sheets. Here, in a case of feeding the sheets S1, first, air isblown to the trailing edge of the upper portion of the sheet bundle Saby the fan 30, so that end portions of the sheets are floated up (liftedby the blown air). After that, the uppermost sheet S1 of the sheetbundle Sa stacked on the sheet stacking board 55 is fed out by thepickup roller 51, and after that, the sheets in the sheet bundle Sa areseparated one by one by the separation portion, followed by feeding, andfurther, are conveyed to the printer main body 1A by the conveyor roller54.

By the way, as illustrated in FIG. 2, the side regulating plates 57 and58 are provided with, a pair of separation claws 101 and 102, which arearranged so as to be engaged with both corner portions as both endportions of the leading edges (downstream edges in the sheet feedingdirection) of the sheets in the width direction. Those separation claws101 and 102 separate the sheets by using deflection of the sheets, whichis caused by stiffness thereof. Specifically, when the each of sheets isfed out by the pickup roller 51, both corner portions of the leadingedge of the sheet are restrained by the separation claws 101 and 102,and the sheet in which the leading edge is restrained is deflected atboth corner portions. When the deflection reaches a predetermined amountor more, the leading edge flicks and climbs over the separation claws101 and 102. As a result, one sheet is separated from the others. Notethat, upward movements of the separation claws 101 and 102 arerestricted by stoppers 57 a and 58 a so that the separation claws 101and 102 can flick out one sheet while deflecting the one sheet at thetime of the separation thereof. The stoppers 57 a and 58 a are formed onthe side regulating plates 57 and 58 in this embodiment. Further, afterelastically flicking out of the separation claws 101 and 102 asdescribed above, the sheet S is fed to the separation portion includingthe feed roller 52 and the retard roller 53.

Here, in this embodiment, the separation claws 101 and 102 are providedto the side regulating plates 57 and 58 so as to be swingable (movable)in the up-and-down direction through a swing shaft (not shown). Further,on the side regulating plate 58 as one of the pair, the photosensor 61is provided, which is a detecting portion configured to detect that theuppermost sheet S1 of the sheet bundle Sa has reached the sheet feedingposition. Note that, in a case where the uppermost sheet S1 has reachedthe sheet feeding position as described above, when the uppermost sheetS1 is fed by the pickup roller 51, the uppermost sheet S1 can smoothlyenter a nip (hereinafter referred to as a separation nip) between thefeed roller 52 and the retard roller 53. Further, on one-side swing endsof the separation claws 101 and 102, claw portions 101 a and 102 a whichare engaged with corner portions of the sheets are provided. Further, inthis embodiment, on the other-side swing end of the separation claw 101as one of the pair, a sensor light shielding portion 101 b configured toshield sensor light of the photosensor 61 is provided.

Here, in this embodiment, in the separation claws 101 and 102, the clawportions 101 a and 102 a are located at lower positions until the sheetstacking board 55 is raised. At this time, the sensor light shieldingportion 101 b of the separation claw 101 as one of the pair has moved toa position of not shielding the sensor light of the photosensor 61, theposition being located above the photosensor 61. In this state, when thesheet stacking board 55 is raised, the corner portions of the uppermostsheet S1 and the claw portions 101 a and 102 a are shortly engaged witheach other, and after that, the separation claws 101 and 102 swing whilethe claw portions 101 a and 102 a are raised together with the sheets onthe sheet stacking board.

When the separation claws 101 and 102 swing as described above, theseparation claws 101 and 102 move in time to separation positions ofseparating the sheets fed by the pickup roller 51. At the separationpositions, the separation claws 101 and 102 abut against theabove-mentioned stoppers 57 a and 58 a which restrict the upwardmovement thereof. Then, when the separation claws 101 and 102 move tothe separation positions as described above, the sensor light shieldingportion 101 b provided on the separation claw 101 shields the sensorlight of the photosensor 61, and the photosensor 61 outputs a triggersignal. Based on this trigger signal, the control portion C determinesthat the uppermost sheet S1 has moved to the sheet feeding position, andstops the raising and lowering motor ML, to thereby stop the rise of thesheet stacking board 55. In this manner, the sheet feeding deck 2completes feeding preparation thereof, and turns to a standby state.When a feeding start signal is sent from the printer main body 1A to thesheet feeding deck 2 after the sheet feeding deck 2 turns to the standbystate, the control portion C controls the drive motor Md of the feedingportion of the sheet feeding deck 2, and rotates the pickup roller 51,to thereby start a feeding operation of the sheet. At this time, thedrive of the fan 30 is started, and air is blown to the trailing edge ofthe upper portion of the sheet bundle Sa on the sheet stacking board, sothat adherence between the uppermost sheet S1 and the sheet in thevicinity thereof is released.

By the way, the sheet feeding operation is repeated so that the sheetsare sequentially fed, with the result that a height of the sheet bundleSa is lowered, and following this, the separation claws 101 and 102gradually swing in a direction in which the claw portions 101 a and 102a lower. Then, when the separation claws 101 and 102 swing as describedabove, the sensor light shielding portion 101 b provided on theseparation claw 101 is raised, and then, becomes unshielding the sensorlight of the photosensor 61. In this manner, the control portion Cdetects that the uppermost sheet S1 has lowered in position than thesheet feeding position, and drives the raising and lowering motor ML ofthe raising and lowering mechanism 60 to raise the sheet stacking board55 so that the uppermost sheet S1 can be maintained at the sheet feedingposition. Though the sheets in the vicinity of the uppermost sheet turnto a state of floating upward due to an influence of air blown theretofrom the fan 30 at this time, the leading edge portions of the sheets,on which the separation claws 101 and 102 are arranged, andparticularly, the corner portions of the sheets are held in a state ofbeing adhered to one another by weight of the separation claws 101 and102. Specifically, in this embodiment, the separation claws 101 and 102also have a function to hold down the sheets for the purpose ofsuppressing the flotation of the leading edge portions of the sheets byair blown thereto by the fan 30. In other words, even in a case whereair is blown to the separation claws 101 and 102, the positions of theseparation claws 101 and 102 are not changed. Accordingly, if thepositions of the separation claws 101 and 102 are detected, then theuppermost sheet S1 can be maintained at the sheet feeding positionwithout being affected by the air.

As described above, in this embodiment, when the sheet stacking board 55is raised, the separation claws 101 and 102 which have moved to theseparation positions are detected, so that it can be surely detectedthat the uppermost sheet has reached the sheet feeding position. Inother words, when the sheet stacking board 55 is raised, it is detectedthat the separation claws 101 and 102 have moved to the separationpositions, so that it can be surely detected that the uppermost sheethas reached the sheet feeding position. Further, the sensor lightshielding portion 101 b is provided on any one of the separation claws101 and 102 as in this embodiment, to thereby increase an amount of thestacked sheets as compared with the case of providing the sensor lightshielding portion above the sheets. Further, in this embodiment, thephotosensor is used for detecting the position of the uppermost sheet,however, other detection units may also be applicable as long as similareffects can be obtained.

Though the sheets are separated by the separation claws 101 and 102 inthis embodiment, the sheets do not sometimes come out of the separationclaws 101 and 102 if engaging amounts of the separation claws 101 and102 with respect to the sheets are increased. Therefore, in order thatthe sheets can surely come out of the separation claws 101 and 102, itis preferred to reduce the engaging amounts of the separation claws 101and 102 with respect to the sheets. However, preferred engaging amountsdiffer depending on types of the sheets. For example, in a case ofspecial sheets such as label sheets, which are perforated, if theengaging amounts of the separation claws are reduced, such sheets areprone to be bent at perforated portions. Therefore, at the time offeeding the special sheets, the sheets cannot push back reaction forcecoming from the separation claws 101 and 102 to thereby cause bucklingon the perforated portions, leading to a feeding failure.

Accordingly, in this embodiment, the perforated portions of theperforated special sheets are covered with the separation claws 101 and102, so that the reaction force coming from the separation claws 101 and102 may be received by portions other than the perforated portions. Inthis embodiment, for example, as illustrated in FIG. 4, an engagingamount Wb of the separation claw 101 in the sheet feeding direction isset at 3.5 times or more an engaging amount Wa thereof in the sheetwidth direction. The same applies to the separation claw 102 as theother of the pair. Further, as illustrated in FIG. 2, the pickup roller51 is provided in the vicinity of the center in the width directionbetween the pair of separation claws 101 and 102, and distances forensuring a sufficient sheet deflection amount are set between the pickuproller 51 and the separation claw 101 and between the pickup roller 51and the separation claws 102. With such a configuration, even theperforated special sheets are not buckled at the perforated portions,and can be stably separated and fed.

By the way, in the description above, the positions of the separationclaws are detected, to thereby hold the uppermost sheet at the sheetfeeding position without being affected by air blown from the fan 30.However, the present invention is not limited to this. For example, insome cases, sheets of which leading edges are curled are stacked on thesheet stacking board. At this time, the height of the sheet surfaceagainst which the sensor flag abuts and the height of the sheet surfaceat the leading edges of the sheets differ from each other as alreadymentioned. In this case, if the height of the sheet stacking board 55 iscontrolled based on the signal coming from the photosensor, the heightof the leading edges is located more upward than a nip (hereinafterreferred to as a separation nip) between the feed roller 52 and theretard roller 53, for example, in a case where the leading edges of thesheets are curled upward. When the sheets are fed in this state, theleading edges of the sheets cannot smoothly enter the separation nip.However, even in a case of feeding the sheets in which the leading edgesare curled, the leading edges of the sheets can be allowed to smoothlyenter the separation nip if the positions of the separation claws aredetected.

FIG. 5 is a view illustrating a configuration of a sheet feeding deck asdescribed above as a sheet feeding apparatus according to a secondembodiment of the present invention. In FIG. 5, the same referencesymbols as those already mentioned in FIG. 2 denote the same orequivalent portions. Further, a description of the same operations asthose in the first embodiment is omitted. Here, until the sheet stackingboard 55 is raised, the separation claws 101 and 102 swing so that theclaw portions 101 a and 102 a can be located at lower positions. At thistime, the sensor light shielding portion 101 b of the separation claw101 as one of the pair has moved to the position of not shielding thesensor light of the photosensor 61, the position being located above thephotosensor 61. In this state, when the sheet stacking board 55 israised, for example, the corner portions of the uppermost sheet S1 inwhich the leading edge portion is curled upward and the claw portions101 a and 102 a are engaged with each other, so that the separationclaws 101 and 102 swing in the direction in which the claw portions 101a and 102 a is raised. When the separation claws 101 and 102 swing asdescribed above, the sensor light shielding portion 101 b provided onthe separation claw 101 shields the sensor light of the photosensor 61,and the photosensor 61 outputs the trigger signal.

Then, based on this trigger signal, a control portion (not shown)detects that the uppermost sheet S1 of the stacked sheet bundle Sa ismoved to the sheet feeding position in which the uppermost sheet S1 canbe fed by the pickup roller 51 to smoothly enter the separation nip.Then, the control portion stops the rise of the sheet stacking board 55based on the detection, to thereby complete the feeding preparation.Then, the sheet feeding deck 2 turns to the standby state. Here, in thisembodiment, the separation claws 101 and 102 is raised in accordancewith the rise of the uppermost sheet S1 curled upward, and thus, theposition where the sheet stacking board 55 stops is a position where theleading edge of the sheet can smoothly enter the separation nip.Specifically, in a case of detecting the positions of the separationclaws 101 and 102 as in this embodiment, the sheet stacking board 55 canbe stopped at the position where the leading edge of the sheet cansmoothly enter the separation nip even if the sheet is curled.

In the description above, the position control for the sheet stackingboard 55 is performed based on the position of the separation claw 101as one of the pair. However, the present invention is not limited tothis. For example, as illustrated in FIG. 6, photosensors 61 and 62 maybe provided on the two side regulation plates 57 and 58, respectively,and the sensor light shielding portions 101 b and 102 b may be providedon the other-side swing ends of the two separation claws 101 and 102.Note that, in this case, the wires 60 a and 60 b which support one ofside end portions of the sheet stacking board 55 are wound in or woundoff by a wire winding shaft 65. Further, the wires 60 c and 60 d whichsupport the other side end portion of the sheet stacking board 55 arewound in or wound off by a wire winding shaft 64. Specifically, in acase where the photosensors 61 and 62 are provided to the sideregulating plates 57 and 58, respectively, two raising and loweringmechanisms 60A and 60B are provided in order to raise and lower thesheet stacking board 55.

With the configuration as described above, when the sheet stacking board55 is raised, the claw portions 101 a and 102 a are engaged with thecorner portions of the uppermost sheet S1 in which the leading edgeportion is curled upward, so that the separation claws 101 and 102 swingin the direction in which the claw portions 101 a and 102 a is raisedtogether with the uppermost sheet. When the separation claws 101 and 102swing as descried above, the sensor light shielding portions 101 b and102 b provided on the separation claws 101 and 102 shield the sensorlight of the photosensors 61 and 62, and the photosensors 61 and 62output the trigger signals. Based on the trigger signals, the controlportion stops the raising and lowering mechanisms 60A and 60B, so thatthe sheet stacking board 55 can be stopped at the position where theuppermost sheet S1 reaches the sheet feeding position.

Here, a curl amount sometimes differs between both corners of theleading edge of the sheet. When the sheet is fed in this state, then insome cases, the leading edge of the sheet does not smoothly enter theseparation nip, and the sheet is skew-fed. However, even in a case wherethere is a difference in the curl amount as described above, the driveof the two raising and lowering mechanisms 60A and 60B is individuallystopped in response to the detection of the separation claws 101 and 102by the photosensors 61 and 62, to thereby control a rising and loweringamount of the sheet stacking board 55 in the width direction. With sucha configuration, even in a case where the curl amount differs betweenboth corners of the leading edge of the sheet, both corners of theleading edge of the sheet can be maintained at the sheet feedingposition, and as a result, the leading edge of the sheet can be allowedto smoothly enter the separation nip without skew-feeding the sheet.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2009-181086, filed Aug. 3, 2009, which is hereby incorporated byreference herein in its entirety.

1. A sheet feeding apparatus configured to feed sheets, comprising: arising and lowering sheet supporting portion configured to support thesheets; a raising and lowering mechanism configured to raise and lowerthe sheet supporting portion; a feed roller configured to feed out anuppermost sheet of the sheets supported by the sheet supporting portion;a detecting portion configured to detect the uppermost sheet of thesheets supported by the sheet supporting portion; a separation claw,which is movable up and down and configured to separate, one by one, thesheets fed by the feed roller, by restraining a side end of leadingedges of the sheets in a width direction orthogonal to a sheet feedingdirection; and a control portion configured to control the raising andlowering mechanism based on a detection by the detecting portion,wherein the detecting portion is arranged to detect a position of theseparation claw, and the control portion controls the raising andlowering mechanism based on the detection by the detecting portion sothat the uppermost sheet of the sheets supported by the sheet supportingportion is located at a position of being feedable by the feed roller.2. A sheet feeding apparatus according to claim 1, further comprising anair blowing portion configured to blow air to trailing edges of thesheets supported by the sheet supporting portion, wherein leading edgeportions of the sheets in which the air is blown to the trailing edgesby the air blowing portion are held down by the separation claw.
 3. Asheet feeding apparatus according to claim 1, further comprising a pairof regulating members configured to regulate positions of the sheets inthe width direction, the sheets being supported by the sheet supportingportion, wherein the separation claw is provided on each of the pair ofregulating members so as to move in an up-and-down direction.
 4. A sheetfeeding apparatus according to claim 3, wherein the detecting portion isprovided on each of the pair of regulating members, the raising andlowering mechanism comprises two raising and lowering mechanisms, whichsupport, raise and lower both ends of the sheet supporting portion inthe width direction, respectively, and when raising the sheet supportingportion, the control portion stops drive of each of the two raising andlowering mechanisms in response to detection of the separation claw bythe detecting portion provided on each of the pair of regulatingmembers.
 5. An image forming apparatus comprising a sheet feedingapparatus configured to feed sheets and an image forming portionconfigured to form an image on each of the sheets fed by the sheetfeeding apparatus, the image forming apparatus comprising: a rising andlowering sheet supporting portion configured to support the sheets; araising and lowering mechanism configured to raise and lower the sheetsupporting portion; a feed roller configured to feed out an uppermostsheet of the sheets supported by the sheet supporting portion; adetecting portion configured to detect the uppermost sheet of the sheetssupported by the sheet supporting portion; a separation claw, which ismovable up and down and configured to separate, one by one, the sheetsfed by the feed roller, by restraining a side end portion of leadingedges of the sheets in a width direction orthogonal to a sheet feedingdirection; and a control portion configured to control the raising andlowering mechanism based on a detection by the detecting portion,wherein the detecting portion is arranged to detect a position of theseparation claw, and the control portion controls the raising andlowering mechanism based on the detection by the detecting portion sothat the uppermost sheet of the sheets supported by the sheet supportingportion is located at a position of being feedable by the feed roller.6. An image forming apparatus according to claim 5, further comprisingan air blowing portion configured to blow air to trailing edges of thesheets supported by the sheet supporting portion, wherein leading edgeportions of the sheets in which the air is blown to the trailing edgesby the air blowing portion are held down by the separation claw.
 7. Animage forming apparatus according to claim 5, further comprising a pairof regulating members configured to regulate positions of the sheets inthe width direction, the sheets being supported by the sheet supportingportion, wherein the separation claw is provided on each of the pair ofregulating members so as to move in an up-and-down direction.
 8. Animage forming apparatus according to claim 7, wherein the detectingportion is provided on each of the pair of regulating members, theraising and lowering mechanism comprises two raising and loweringmechanisms, which support, raise and lower both ends of the sheetsupporting portion in the width direction, respectively, and whenraising the sheet supporting portion, the control portion stops drive ofeach of the two raising and lowering mechanisms in response to detectionof the separation claw by the detecting portion provided on each of thepair of regulating members.